1. Field of the Invention
The present invention relates to a Cognitive Radio (CR) system. More particularly, the present invention relates to a method and apparatus for channel management in a CR system supporting multiple channels.
2. Description of the Related Art
Today, with the development of mobile communication technologies, various types of mobile communication systems can coexist while using different frequencies. The various types of mobile communication systems are assigned with different frequency resources to avoid mutual interference. Since the different frequencies cannot be assigned to all mobile communication systems due to limited frequency resources, research for effectively using frequency bands is actively being conducted.
For example, a Cognitive Radio (CR) technique is used to provide a desired communication service by automatically searching for an unused frequency according to an area and a time while protecting an allowed neighboring mobile communication system. That is, the CR technique can determine and utilize a frequency bandwidth, an output power, a modulation scheme, etc., conforming to a current environment by searching for an idle spectrum which is scattered in various widths and in which an occupied time is continuously changed. Thus, efficiency of a limited resource (i.e., frequency) can be increased.
FIG. 1 is a diagram for explaining a concept of a CR communication system according to the prior art.
Referring to FIG. 1, a Tele-Vision (TV) repeater 100 broadcasts a video signal to TV receivers (not shown) located in a service area by using an assigned channel. A first CR system includes Base Stations (BSs) 121, 122, and 123 and provides services to Mobile Stations (MSs) (not shown) located in respective service areas by sharing a channel during a time when the TV repeater 100 does not broadcast through the channel. Likewise, a second CR system includes BSs 130 and 131 and provides services to MSs (not shown) located in respective service areas by sharing a channel during a time when the TV repeater 100 does not broadcast through the channel. The first CR system and the second CR system exchange an available channel list to avoid mutual interference.
A frequency spectrum is divided into multiple slots in order to manage multiple systems (e.g., a TV broadcast system, the first CR system, the second CR system, and a wireless microphone 110) operating in the same frequency band. The slot will be referred to herein as a channel. One channel is a basic unit that is used when a frequency resource is allocated between the multiple systems. For example, the TV broadcast system is designed to provide a broadcast service within a specific region. Assigned broadcast channels are generally distinguished by dividing an allowed frequency band according to a frequency allocation policy. In a Digital TV (DTV) system, a TV frequency range may include around one hundred TV channels. Each channel has a bandwidth of 6, 7, or 8 MHz. A system using the licensed frequency band as in the case of the TV broadcast system is referred to as an incumbent system or a primary system.
As an example of an incumbent system, the wireless microphone 110 is a narrowband communication apparatus and occupies a part of a TV channel. The first CR system and the second CR system can detect a low power, narrowband apparatus and perform communication by avoiding detected channels.
A CR system coexisting with the incumbent system can detect whether a channel is used by the incumbent system, and if the channel is not used by the incumbent system, the CR system performs communication by using the unused channel. In addition, when a currently used channel is reused by the incumbent system, the CR system can stop the use of the channel and switch to an empty channel, thereby maintaining communication.
A conventional CR system operating in a channel unit performs communication using one channel. In other words, the CR system uses only one channel even if one or more available TV channels are detected by the CR system. The CR system uses various schemes supporting multiple channels such as channel bonding, channel aggregation, and Scalable Orthogonal Frequency Division Multiple Access (SOFDMA) schemes. However, there is no channel management technique to be used in a CR system supporting multiple channels.
Accordingly, there is a need for an apparatus and method for channel management in a Cognitive Radio (CR) system supporting multiple channels.